Preheat oven to 350 degrees. In a medium baking dish, spray with non-stick cooking spray. Set aside.
Wash, peel, and boil the sweet potatoes, over medium high heat. (Depending on how large or small they are cut, this takes 14-18 minutes.) To test the potatoes for doneness, pierce with a fork or knife. If the potato piece breaks apart easily, they are done.
Transfer the cooked potatoes to a mixing bowl, and add the brown sugar, half and half, butter, egg, vanilla and salt. Using a potato masher, combine the ingredients and mash until mostly smooth. Small lumps are okay. Transfer the potato mixture to the prepared baking dish.
In a separate bowl, combine the brown sugar, pecans, flour, cinnamon and nutmeg. Stir together to combine. Pour the melted butter into the brown sugar mixture, and stir until crumbly. Sprinkle the pecan crumble evenly over the top of the potatoes, covering completely. Garnish with some pecan halves, if desired. Cover the baking dish loosely with foil.
Bake, covered, at 350 degrees for 35 minutes. Remove the foil and bake for another 10 minutes to allow the pecans to toast. (Total bake time is 45 minutes.)
Remove from oven and let cool slightly before serving. Enjoy!